The present invention relates to the removal of spray-on foam insulation from aerospace structures or systems, and an apparatus capable of removing and collecting fragmented particles of foam insulation, and more particularly relates to an apparatus for removing and collecting fragments of spray-on foam insulation from the interior of an aircraft fuselage.
Insulation is typically provided on the exterior and/or interior of aerospace systems, particularly between the outer bodies and the internal passenger compartments of aircraft fuselages. The insulation provides a number of functions including regulation of temperature, reduction of engine noise, reduction of noise from outside air turbulence, and protection of mechanical and structural components within the aerospace systems from moisture and temperature extremes which might tend to damage or corrode the components.
Until recently, fiberglass batting had been the preferred insulation for use within aircraft and other aerospace structures. Fiberglass has good thermal and structural properties, is fairly inexpensive, and has a long history of successful use in the aerospace industry.
Recently, however, the use of spray-on foam insulation has emerged as an alternative approach for insulating aerospace structures. Spray-on foam insulation, such as polyurethane or polyisocyanurate closed cell foam materials, are polymeric substances containing large volumes of air or other blowing agents dispersed within the polymer. The ability to blow the polymeric foams at the site of installations allows for the quick and easy installation of insulation within an aircraft fuselage or other structure, and the ability of the spray-on foam to flow and solidify around structural members and mechanical components allows more effective insulation of the members and components than previously possible with fiberglass insulation.
One disadvantage to the use of spray-on foam insulation is that, once solidified, the foam is difficult to remove. During the normal operation of an aircraft or spacecraft, routine inspections are made and routine maintenance is performed. Servicing of the aircraft often includes examination of components which have been insulated, which frequently requires removal of the insulation for visual inspection of the underlying structures. The insulation may be physically scraped away from the structure or component which it insulates, but such scraping is time consuming and is likely to cause damage to the underlying components and structures of the aircraft. Thus, physically scraping the insulation is an inefficient method of insulation removal.
It has been found that spray-on foam insulation may be effectively and efficiently removed using carbon dioxide pellet cryogenic blasting, known as dry ice stripping. Dry ice stripping works by projecting small pellets of dry ice, under pressure, toward the foam insulation to be removed. The dry ice impacts the foam at high speed and pulverizes the foam into small particles. The pressure with which the pellets are projected and the angle of impingement of the pellets upon the foam surface are adjusted so that the impacting pellets do not damage the underlying structures. In addition, most of the impact energy of the pellets is absorbed by the foam, leaving the underlying structures unharmed.
A major advantage of using dry ice for foam removal is that the dry ice sublimes after impact, leaving no solid or liquid residue. However, dry ice stripping does result in the fragmentation of the foam insulation, which has the potential to cause foreign object damage (FOD) within the aircraft. Even though removal of the spray-on insulation from the underlying substrate is facilitated by dry ice stripping, removal of the pulverized foam fragments from the area surrounding the removed foam is a painstaking procedure. It has heretofore been impractical to efficiently collect fragmented foam after a dry ice stripping or similar foam removal procedure.
What is needed is an apparatus which provides for the containment and collection of foam fragments after foam insulation has been removed from a substrate using dry ice stripping. The apparatus should provide for the removal of foam fragments and debris from the fuselage of an aircraft or other aerospace system with a minimum of manual labor and a minimum of time expenditure.
The present invention solves the problem associated with collection of foam insulation debris resulting from the rapid removal of spray-on foam insulation from aerospace systems by dry ice stripping or similar processes through use of an apparatus having a containment chamber which is shaped to correspond to the surface structure of the internal portion of an aircraft fuselage. The invented apparatus operates under a pressure differential such that foam fragments generated during a foam removal operation are suctioned and collected by the invented collection/storage apparatus.
The invented containment apparatus primarily comprises a containment chamber which defines a foam inlet, a vacuum draw port, and an air inlet. The containment chamber is a walled structure having one surface that is substantially or completely open, thus defining the foam inlet. The periphery of the foam inlet is shaped to correspond to the internal dimensions or surface structure of an aircraft fuselage. The phrase xe2x80x9caircraft fuselagexe2x80x9d is used throughout as an example of the surface to which the invented apparatus is to be applied. However, it should be recognized that the invented containment apparatus is applicable to any of a variety of surfaces found in aerospace vehicles which are coated with spray-on insulation.
Because the surrounding of the foam inlet corresponds to the shape of the fuselage or other insulated structure, a containment area is formed by mating the containment apparatus with the portion of the fuselage having insulation to be removed or captured such that the apparatus forms a type of seal with the structure and such that insulation being removed from the structure can not migrate out of the containment area. For example, for small insulation removal projects, a smaller vacuum chamber may be used, with the surrounding of the foam inlet corresponding to and fitting around supporting members of the fuselage frame. For larger insulation removal projects, a large vacuum chamber may be used, with the surrounding of the foam inlet corresponding to and fitting within the general cylindrical diameter of the tubular fuselage. By utilizing a vacuum chamber which corresponds to the structure of the fuselage, there are few or no gaps between the vacuum chamber and the fuselage structure during operation of the apparatus once the apparatus is mated with the fuselage surface.
The vacuum port is connected to the containment chamber and is used to facilitate connection to a vacuum source. The vacuum port is generally a tubular structure having a proximal end connected to the containment chamber and a distal end for connection to a vacuum source. The proximal end of the vacuum port is typically a circular or oval opening, and is a minimum of 7 inches in diameter so that large foam particles, many of which are over 2 inches in diameter, may be suctioned through the vacuum port without impairing air flow. The distal end of the vacuum port is also a minimum of 7 inches in diameter so that the foam particles may be transported completely through the port. Also, the distal end of the vacuum port is typically of standard dimensions so that it may be connectable to industrially available vacuum components.
The air inlet is provided in or through a wall of the containment chamber. The air inlet may be a simple hole or tube provided through a wall in the containment chamber or the air inlet may be provided by one or more of the walls of the containment chamber being of a porous material. Whatever the configuration of the air inlet, the purpose of the air inlet is to prevent a strict vacuum condition from forming within the containment chamber which might impair the flow of air and insulation particles through the apparatus. For instance, if a strict vacuum were formed by sealing the containment chamber against an aluminum or foam surface, then no transfer or removal of foam would take place because there would be no air flow in which to carry the foam residue. To prevent this condition, the air inlet provides a continuous stream of flowing air within the containment chamber, thus providing a vehicle to carry foam particles away from the insulated surface, through the vacuum port, and eventually to a particle storage system.
By utilizing the invented foam containment apparatus in conjunction with a rapid foam removal process such as dry ice stripping, particulate foam insulation is effectively removed from the fuselage of an aircraft or other aerospace structure without contaminating the aircraft or structure and causing foreign object damage.